In many industries, the forming of thermoplastic annular articles is important. One case, is the fabrication of solid elastomer baby carriage tires. The nature of the market is such that the tires must be made very inexpensively, yet a pleasing appearance is quite important. Injection molding of the tires is an expensive operation which severely limits the cross-sectional shape of the product. An important shape embellishment is the provision of circumferential grooves in the outside surface or tread of the tire. These grooves are not only desirable for appearance, but also result in a smooth rolling tire. They are, however, quite difficult to form using molding techniques. It is felt that a method which should give good results would be the combination of extruding material in a non-circular cross-section, cutting off suitable lengths, and uniting the ends to form a ring. The equipment which has been provided in the past for performing such tasks have been plagued with problems. Uniting the two ends of a workpiece of non-circular cross-section without providing for maintenance of good registration, i.e., shape-to-shape conformance has resulted in an unsightly and out-of-round "score." Furthermore, the old methods of melting the workpiece ends to make a bond has resulted in deformation and the formation of "flash." Another factor in ring formation is that the forming operation is best carried out where the workpiece is fresh from the extruder. Synchronizing a discrete operation like this method of wheel formation with a continuous operation like extrusion must be accomplished for an efficiently operating machine.
These and other difficulties experienced with the prior art apparatus have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a machine for uniting the two ends of an elongated piece of thermoplastic material to form a ring or annulus.
Another object of this invention is the provision of a machine adapted to transform a continuously-extruded material into annular rings.
A further object of the present invention is the provision of a machine for forming rings from linear material by uniting the ends so that accurate registration of non-circular cross-sections is achieved.
It is another object of the instant invention to provide a machine for connecting pieces of thermoplastic material without forming flash.
A still further object of the invention is the provision of a machine for forming rings in which the finished ring can be simply allowed to fall from the work area without interference with portions of the machine.
It is a further object of the invention to provide a machine for forming rings which is of such simplicity that its initial and maintenance cost are low.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.